Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.99	8.123%	$99.4623	$99.46	$99.45	$99.50
Purchase #2	$112.60	9.585%	$123.3927	$123.39	$123.40	$123.40
Purchase #3	$200.83	13.360%	$227.6609	$227.66	$227.65	$227.70
Purchase #4	$33.38	13.301%	$37.8199	$37.82	$37.80	$37.80
Purchase #5	$134.88	7.560%	$145.0769	$145.08	$145.10	$145.10
Purchase #6	$36.51	12.226%	$40.9737	$40.97	$40.95	$41.00
Purchase #7	$95.59	8.820%	$104.021	$104.02	$104.00	$104.00
7 purchase totals =	$705.78		$778.4074	$778.40	$778.35	$778.50